Digitalizing the skull of Saurosuchus galilei (Archosauria: Pseudosuchia): First reconstruction of the nasal cavity and osteological notes

ULLOA-GUAIQUIN, K.; VON BACZKO, M. B.; CARDILLO, ARIEL F.; PAULINA CARABAJAL, A.; DESOJO, J.B.

Salta

Congreso; Reunión de Comunicaciones de la Asociación Paleontologica Argentina; 2022

Asociación Paleontologica Argentina

During the Late Triassic of Argentina, the continental tetrapod diversity is mainly represented by archosauriforms like Proterochampsia, Aetosauria, Erpetosuchidae, Ornithosuchidae, Poposauroidea, and Loricata, among others sauropsids. Saurosuchus galilei Reig 1959 is a quadrupedal, short-necked large basal loricatan (Pseudosuchia) recovered from the Ischigualasto Formation (Ischigualasto-Villa Union Basin, Argentina) that occupies a hypercarnivorous role in the complex continental triassic faunal association. Currently, the skull materials of Saurosuchus are limited to two crania, the holotype (Instituto Miguel Lillo, Tucumán, Argentina, PVL 2062) and a referred material (Division of Vertebrate Paleontology of the Museo de Ciencias Naturales de la Universidad Nacional de San Juan, Argentina, PVSJ 32). PVL 2062 preserves the laterally compressed partial sides of the skull, described by Reig in 1959. In contrast, PVSJ 32 preserves the almost complete articulated skull, which was described by Alcober in 2000. Here, we present a three-dimensional model of the skull and nasal cavity of PVSJ 32 based on computed tomography. Novel anatomical information added to the original description includes the suture of both anterodorsal and posterodorsal premaxilla processes with the nasal, and the sutures of the palpebral/postfrontal with the prefrontal, frontal, and postorbital. In the braincase, the sutures of the supraoccipital with the otoccipital, prootic, and laterosphenoids; and the basioccipital-basisphenoid suture are also observed. The 3D model of the nasal cavity has three anatomical regions, the vestibule, the nasal cavity proper (cavum nasi propium), and the nasopharyngeal duct. In S. galilei there is a short vestibule, more similar to that of carnivorous dinosaurs than that of the more closely related extant pseudosuchians, the crocodiles. The nasal cavity proper comprises two-thirds of the skull length. The main part, the cavum, housed the olfactory and respiratory regions. The olfactory region occupies a notable portion with an anteroposterior tubular form that extends dorsally from the middle of the nasal bone until the anterior margin of the frontal bone, where the olfactory bulbs are located. The respiratory region connects with a poorly marked nasopharyngeal duct. In ventral view, choanae are positioned in the anterior portion of the palate and have a margin limited posteriorly by both palatines, and medially by both vomers that does not preserve their anterior portion. This new information about the osteology and nasal cavity support the actual hypothesis regarding the habit of this form. Furthermore, for the first time in a basal Loricata, it will allow us to make paleobiological inferences regarding aspects such as olfactory acuity and thermoregulation of this top predator.